diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7a3201e..e2fd243 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -23,7 +23,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Configure
-        run: cmake -S . -B build -DCMAKE_BUILD_TYPE=Release -DTAP_DSP_WERROR=ON
+        run: cmake -S . -B build -DCMAKE_BUILD_TYPE=Release -DTAP_DSP_WERROR=ON -DTAP_DSP_BUILD_CAPI=ON
 
       - name: Build
         run: cmake --build build --config Release
diff --git a/.gitignore b/.gitignore
index 993115e..6590f84 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,3 +8,4 @@ CMakeUserPresets.json
 !.claude/settings.json
 !.claude/hooks/
 build_capi/
+__pycache__/
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7d7d5f3..99ae77a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -132,3 +132,14 @@ if(TAP_DSP_BUILD_TESTS)
     enable_testing()
     add_subdirectory(tests)
 endif()
+
+# C ABI shared library for FFI consumers (the notebooks drive the shipping C++
+# through it via ctypes — see notebooks/dsptap_py.py). tools/capi also builds
+# standalone (`cmake -B build_capi -S tools/capi`), which is what the ctypes
+# bridge does on first import; this option exists so the root build can compile
+# it too, matching the BUILD_CAPI option every sibling library carries. CI turns
+# it on so the verification layer cannot rot unnoticed.
+option(TAP_DSP_BUILD_CAPI "Build the C ABI shared library" OFF)
+if(TAP_DSP_BUILD_CAPI)
+    add_subdirectory(tools/capi)
+endif()
diff --git a/notebooks/__pycache__/dsptap_py.cpython-311.pyc b/notebooks/__pycache__/dsptap_py.cpython-311.pyc
deleted file mode 100644
index a544978..0000000
Binary files a/notebooks/__pycache__/dsptap_py.cpython-311.pyc and /dev/null differ